1. Field of the Invention
The present invention concerns improvements in traveling bridge filtering systems. More particularly, it concerns methods and improved apparatus for automatically controlling the backwash cycle and permeability of the filter bed in such systems.
2. Description of Related Art
The traveling bridge filter system has proven to be quite efficient, cost effective and durable in certain applications. The art is exemplified in U.S. Pat. Nos. 3,239,061 and 4,152,265 and further exemplified in assignee's brochure, Clean Water for Less, Copyright 1991.
A principal use of a traveling bridge filter system is the removal of suspended material or solids from a liquid influent in order to meet governmental regulatory requirements. In recent Years, regulatory requirements have become more stringent, making filtering system efficiency and reliability a paramount concern.
Presently, filters of this type initiate a backwash whenever the influent level in the filter bed reaches a predetermined and fixed elevation. During the backwash cycle, a traveling bridge backwash mechanism is commenced to move, cell by cell, from one end of the filter bed to the opposite end. Once the backwash mechanism reaches the opposite end of the bed, if the water level in the bed has fallen below a given elevation, also predetermined and fixed, the backwash cycle terminates. If the water level in the filter bed has not fallen below the predetermined fixed elevation, the backwash mechanism will continue to operate, traveling cell by cell from one end of the filter bed to the other, until an operator intervenes, or until, when the backwash mechanism is at one end of the bed, the water level has fallen below the predetermined elevation. This is a very limited method of backwash control.
It is known that in traveling bridge filter systems fluctuating flow rates and solids loading are a commonplace occurrence. Higher hydraulic loading alone typically results in higher water levels in the filter bed even when the filtration media is clean. With their limited method of backwash control, current filters are unable to distinguish between conditions that develop as a result of solids versus hydraulic loading. Thus, current filters initiate a backwash cycle even when insufficient solids have been deposited to warrant media cleansing. This is an undesirable and limited method of backwash control that adversely effects the efficiency, cost-effectiveness, permeability and throughput performance of the filter bed system.
It is widely known by those familiar with the art that over time a mat of solids develops on the surface of the filter media schmutzdecke resulting in beneficial and substantial solids removal as well as detrimental and substantial headloss. As the quantity of material forming the mat increases, the permeability of the filter bed decreases. Removal of the entire mat by backwashing, however, is not desired since within limits, the solids removal efficiency and effluent or filtrate quality are directly related to the quantity of material forming the mat.
Current methods of backwashing filter beds result in excessive and unnecessary backwash usage and impair filter performance by removing excessive solids thereby damaging the mat of solids which is so influential in optimizing filter performance.
A principal object of the present invention is the improvement of traveling bridge filter systems vis-a-vis new apparatus and methods for automatically controlling the backwash cycle and the permeability of the filter bed by evaluating dynamic hydraulic and solids loading conditions, initiating and controlling the backwash cycle and executing automatic adjustments to maintain the highest filtering efficiency possible, without operator intervention.
A further object is the automatic optimization of filter throughput.
The detailed description discloses the preferred embodiments of the invention however, various changes and modifications to the preferred embodiments are within the spirit and scope of the invention.